Add check for the 'sigaction' function

This check is easier to get in autoconf than a test for struct sigaction.
It's also more complete, since the recorder actually needs the function.

config/check_sigaction.c

@@ -0,0 +1,8 @@
+#include <signal.h>
+
+int main()
+{
+    struct sigaction sa;
+    sigaction(11, &sa, NULL);
+    return 0;
+}